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<h2><a name="SECTION0018120000000000000000"></a><a name="posix-contents"></a>
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16.1.2 Module Contents 
</h2>

<p>
Module <tt class="module">posix</tt> defines the following data item:

<p>
<dl><dt><b><tt id='l2h-3515' xml:id='l2h-3515'>environ</tt></b></dt>
<dd>
A dictionary representing the string environment at the time the
interpreter was started. For example, <code>environ['HOME']</code> is the
pathname of your home directory, equivalent to
<code>getenv("HOME")</code> in C.

<p>
Modifying this dictionary does not affect the string environment
passed on by <tt class="function">execv()</tt>, <tt class="function">popen()</tt> or
<tt class="function">system()</tt>; if you need to change the environment, pass
<code>environ</code> to <tt class="function">execve()</tt> or add variable assignments and
export statements to the command string for <tt class="function">system()</tt> or
<tt class="function">popen()</tt>.

<p>
<span class="note"><b class="label">Note:</b>
The <tt class="module"><a href="module-os.html">os</a></tt> module provides an alternate
implementation of <code>environ</code> which updates the environment on
modification.  Note also that updating <code>os.environ</code> will render
this dictionary obsolete.  Use of the <tt class="module"><a href="module-os.html">os</a></tt> module version of
this is recommended over direct access to the <tt class="module">posix</tt> module.</span>
</dd></dl>

<p>
Additional contents of this module should only be accessed via the
<tt class="module"><a href="module-os.html">os</a></tt> module; refer to the documentation for that module for
further information.

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<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
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